why it is not necessary to take undo backup?

You know…it is not necessary to take undo tablespace backup either in cold backup or hot backup. But ofcourse many of DBA’s will include that in their script…

Now a big question…if undo is not being backed up and lets say i need to do instance recovery or database recovery and need to rollback a transaction, how that will happen.

Here is the answer…

when you do some transaction, redo entries will be generated..accepted ! Just like that whenever some changes happend to undo tablespace (or more clearly undo segments) oracle will generate redo entries.

So even though you doesn’t backup undo, you have the redo entries through which you can recover or rollback the transactions.